Hot tops and mixture of materials therefor

ABSTRACT

THE BASIC IDEA OF THE INVENTION IS TO PROVIDE A WALL MATERIAL FOR THE HOT TOP HAVING SUCH A COMPOSITION THAT THE SURFACE CONTACTING THE MOLTEN STEEL OR OTHER METAL WILL BE COVERED WITH A SMOOTH, GASTIGHT, THIN, VITREOUS MINERALIC LAYER WHEN CONTACTING THE MOLTEN STEEL OR METAL. THE WALL MATERIAL IS MADE FROM A MIXTURE OF GRANULAR OR POWDERED AERATED CONCRETE OR POROUS CONCRETE AND ORGANIC FIBRE MATERIAL SUCH AS WOOD MEAL, SAWDUST, MECHANICAL WOOD PULP AND A BINDER, AND ACCORDING TO THE INVENTION THE MIXTURE ALSO COMPRISES SAND OF SUCH A RATE OF REFRACTABILITY THAT THE MELTING TEMPERATURE OF THE SAND IS LOWER THAN THE TEMPERATURE OF THE MOLTEN METAL, SAID SAND, UNDER THE INFLUENCE OF THE HEAT FROM THE MOLTEN METAL, PROVIDING A THIN VITREOUS MINERALIC LAYER.

Patented Dec. 19, 1972 3,706,682 HOT TOPS AND MIXTURE OF MATERIALS THEREFOR Berti! Hilmer Allvin, Asgatan, Sweden, assignor to Enn Vallak, Geneva, Switzerland No Drawing. Filed Jan. 25, 1971, Ser. No. 109,647 Claims priority, application Sweden, Feb. 2, 1970, 1,322 Int. Cl. B28b 7/36; C08f 45/18 US. Cl. 26017.2 4 Claims ABSTRACT OF THE DISCLOSURE The basic idea of the invention is to provide a wall material for the hot top having such a composition that the surface contacting the molten steel or other metal will be covered with a smooth, gastight, thin, vitreous mineralic layer when contacting the molten steel or metal. The wall material is made from a mixture of granular or powdered aerated concrete or porous concrete and organic fibre material such as Wood meal, sawdust, mechanical wood pulp and a binder, and according to the invention the mixture also comprises sand of such a rate of refractability that the melting temperature of the sand is lower than the temperature of the molten metal, said sand, under the influence of the heat from the molten metal, providing a thin vitreous mineralic layer.

This invention relates to hot tops for casting steel and to a Wall material particularly suited to such hot tops.

It is already known to manufacture hot tops from exothermic, combustible, ceramic and refractory material. Furthermore, it is known to manufacture hot tops from porous insulating materials such as aerated concrete, kieselguhr, asbestos or vermiculite and to provide these hot tops, on the side facing the steel or metal, with a surface layer of refractory material such as chamotte meal, quartzite powder or dolomite powder.

Most hot top constructions which have come onto the market during recent years are notable in that they substantially consist either of refractory material or are equipped with a surface layer of refractory material.

Since the molten steel when tapped into the chill has a temperature of between -1600" C. it is natural that in constructing hot tops an effort should be made to use material having as high a melting point as possible in order to prevent the material of the hot top from melting. For this reason refractory material such as quartzite powder, dolomite powder, etc., is often used.

The drawback of all the hot tops at present on the market is that after stripping of the ingot remnants or residuals of the hot top remain on the ingot and may give rise to surface defects when the ingot is rolled. Furthermore, with the present refractory or combustible hot tops, surface segregation often occurs on the upper part of the ingot. This necessitates expensive finishing steps such as grinding. The invention aims at avoiding these disadvantages.

The basic idea of the invention is to provide a wall material for the hot top having such a composition that the surface contacting the molten steel or other metal will be covered with a smooth, gastight, thin vitreous mineralic layer when contacting the molten steel or metal.

In performing the invention the wall material of the hot top is made from a mixture of granular or powdered aerated concrete or porous concrete and organic fibre material such as wood meal, sawdust, mechanical wood pulp and a binder, and according to the invention the mixture also comprises sand of such a rate of refractability that melting temperature of the sand is lower than the temperature of the molten metal, said sand, under the influence of the heat from the molten metal, will define a thin vitrous, mineralic layer. The sand may, for example contain felspar, preferably having finer particles than the aerated concrete. As a rule, the upper limit of the melting temperature or melting temperature interval of the steel is 1570-1610 C. The liquidus temperature (melting temperature interval) of the steel may vary, for example, between 1450 and 1550 C. Thus, the melting temperature of the sand should be lower than this lquidus temperature or melting temperature interval. When the sand material contacts the molten-hot steel or metal, the sand at the contacting surface melts and the vitreous melt formed by the sand will be partially absorbed by the coarser particles of aerated concrete there so that a thin layer of vitreous mineralic material will be formed. The melting process is limited to a thin zone since the vitreous mineralic layer contains a large number of porous relatively coarse concrete particles which render the vitreous layer extremely heat-insulating and since a large number of such coarser, unmelted grains of porous concrete in the vitreous layer will cause the melting point of the vitreous layer to be much higher than the average analysis of the ceramics would in fact indicate.

The vitreous layer will protect the steel or metal against carburization and other impurities and will impart a smooth surface to the hot top and the billet. Normally no remnants of the hot top will stick to the resultant smooth casting or billet surface. The heat radiation from the smooth surface will also become less than from the normal, somewhat rough surface.

Suitable particle sizes are, for non-refractory sand of the kind now defined, max. 1.5 mm. and at least lower than 0.5 mm. and for porous concrete max. 6 mm. and at least 80% lower than 3 mm. Thus, preferably, the particle size of the porous concrete exceeds that of the sand. The ratio by weight between sand and porous concrete should be between 1:2 and 4:1, suitably 2:1. The best quantity of sawdust or other organic fibre material is between 5-10% by weight. Preferably the binder should be of organic nature. An extremely suitable binder is an emulsion of polyvinyl acetate. It can be used alone, but can also very well be combined with dextrine, molasses, sulphite lye, core oil and phenolic resins.

Hot tops made in one integral piece or in the form of slabs of this material can be manufactured by mixing the dry materials with binder in conventional way and then pressing the mixture in moulds. The material is then allowed to dry in a drying furnace at 200 C. It is possible to produce hot top material having a low volume weight as low as 0.7-0.8 g./cm. which means an extremely high insulating capacity.

What I claim is:

1. Wall material for hot tops for chill casting of steel or other metal, said material comprising a mixture of granular and powdered porous concrete having a particle size not exceeding about 6 mm., at least one of a group of organic fibre materials selected from wood meal, sawdust and mechanical wood pulp, a binder for said organic fibre material comprising an emulsion of polyvinyl acetate, and sand having a particle size not exceeding about 0.5 mm., said organic fibre material comprising between 5% and 10% by weight of the entire mixture, the ratio by weight of sand to porous concrete being between 1:2 and 4:1, the ratio of refractability of said sand being such that the melting temperature of the sand is lower than the temperature of the molten metal, said sand, under the influence of heat from the molten metal, providing a thin vitreous, mineralic layer at the surface of the wall material contacting the molten metal.

2. The material of claim 1 wherein said binder consists of an emulsion of polyvinyl acetate combined with an element from the group consisting of dextrine, molasses, sulphitic lye, core oil and phenolic resin.

3. The material of claim 1 wherein the ratio by weight of sand to porous concrete is about 2:1.

4. Material according to claim 1, shaped into a hot top for chill moulds.

5 References Cited FOREIGN PATENTS 753,789 8/1956 Great Britain 106-383 162,938 4/1958 Sweden 10638.3

10 WILLIAM H. SHORT, Primary Examiner E. WOODBERRY, Assistant Examiner US. Cl. X.R. 

